Radio receiver



Feb. 2, 1937.

K. A. CHITTICK ET AL RADIO RECEIVER Fild Sept. 50, 1955 2 Sheets-Sheet 1 POWER 53 89 l SUPPLY 1 0 87 To macs/As William HConron INVENTORSY Kenneth A.Chiilicl'i BY WMM Q Feb. 2, 1937. K. A. CHlTTlCK ET AL RADIO RECEIVER Filed Sept. 50, 1953 2 Sheets-Sheet 2 INVENTORS KennethH.Cl-aitticli William H. Conron Patented Feb. 2, 1937 UNITED STATES PATENT OFFICE RADIO RECEIVER ware Application September 30, 1933, Serial No. 691,590

Claims.

Our invention relates to radio receivers, and more particularly to radio receivers of the multi- Wave type adapted to receive radio signals over a plurality of wave bands or frequency ranges.

In providing for multi-wave reception, and notably for broadcast and short wave reception, various circuits have been utilized for adapting a radio receiver, designed primarily for reception within the broadcast band, to receive signals within the different frequency or Wave band, such as a short wave band or bands. One such circuit for adapting an existing broadcast receiver for short wave reception is represented by the well known short-wave converter ordinarily comprising an oscillator and .one or more tuned radiofrequency circuits in connection with a detector which may be connected to a conventional broadcast receiver at the proper point in the circuit. In connection with the present popular superheterodyne type of radio receiver, the high fre-- quency or short-wave signals are converted to either the radio or to the intermediate frequency for which the broadcast receiver is designed.

The converter type of circuit, while generally satisfactory in operation, with a certain required degree of understanding and skill on the part of the operator of the apparatus in which it is included involves considerable extra apparatus and cost together with extra tuning controls, thereby limiting its commercial use.

Another type of circuit involves switching or plugging into circuit, one or more sets of coils for differing wave band reception. In a superheterodyne receiver this may involve such changes in three different circuits, the radiofrequency, the detector, and the oscillator circuits, for the different frequency ranges or wave bands to be received. The objectionable features of this type of circuit are well known.

It is a primary object of our invention, therefore, to provide a simplified, unitary receiver for operation over a plurality of frequency or wave bands which obviates the above named and other disadvantages inherent in prior receivers of that type.

A further object of our invention is to provide a receiver of theabove-mentioned type which is tunable over a wide frequency range within said frequency bands.

A further object of our invention is to provide -a superheterodyne receiver of the above-mentioned type, and one which does not require a major change in the fundamental circuit constants of the oscillator when switching'from .one frequency range to another, whereby the liningup of the oscillator and the tuned radio-fre quency circuits is facilitated.

A still further object of our invention is to provide an improved method and means for lining-up the tuned radio-frequency circuits and the oscillator circuit in the different frequency ranges of a multirange superheterodyne receiver.

In practicing one embodiment of our invention we design the receiver to receive signals both within a band from 540 kilocycles to 1500 kilocycles, which will be referred to as the broadcast band, and Within a band from 1255 kilocycles to 3000 kilocycles, which will be referred to as the police band.

Reception within the police band is accomplished by utilizing the second harmonic of the superheterodyne oscillator and by short-circuiting a portion of the inductance coil in each tuned radio-frequency circuit to make the circuit .tunable over the police band with the same variable tuning means.

Other features and advantages of our invention will appear from the following description taken in connection with the accompanying drawings in which Fig. 1 is a circuit diagram of a radio receiver embodying our invention;

Fig. 2 is a similar circuit diagram of the receiver of Fig. 1, showing in perspective a preferred form of switching mechanism, and tuning coil units for the tuned circuits thereof; and

Figs. 3, 4 and 5 are circuit diagrams showing modifications of certain .of the tunedcircuits of Figs. 1 and 2, and illustrating modifications of the invention.

Referring to Fig. 1, one embodiment of our invention comprises a tuned radio frequency amplifier which includes a vacuum tube ll having an indirectly heated cathode I3, a control grid I5, a screen grid IT, a suppressor grid l9, and an anode 2|. The tuned input or selecting circuit 23 for the vacuum tube H comprises a radio frequency transformer 25 having a primary winding 2.! and. a secondary winding 29. The upper end of the primary winding .21 is connected to an antenna 3|, while the lower end of the winding is connected to ground.

The secondary winding 29 is shunted by a variable condenser 33 which is one unit of a gang condenser. Condenser 33 is shunted by a trimmer condenser 35 for use in lining-up the several tuned circuits in the usual manner. The tuned circuit thus formed is connected across the input electrodes of the vacuum tube l l by means of a conductor 3! connecting the upper end of the secondary winding 29 to the control grid I5, and a condenser 39 connecting the grounded lower end of the secondary winding 29 to the cathode I3.

The circuit as above described is tunable over the broadcast band. In order to make the radio frequency circuit 23 tunable over a higher frequency range, in this case the above mentioned police band, a switch M is provided for shorting a portion of the secondary winding 29. Another switch 43 is provided for shunting a second trimmer condenser 45 across the tuning condenser 33 at the same time that the secondary portion 29 is shorted, the condenser 45 being for the pur pose of lining-up the tuned circuits in the police band.

The switch 43 performs an additional function in that, when closed, it connects a small coupling condenser 47 between the upper end of the primary winding 21 and the upper end of the secondary winding 29, the coupling condenser 4! being for the purpose of maintaining'the transfer of energy from the primary winding to the tuned circuit 23 at the desired value in the high frequency or police band.

The output circuit of the amplifier tube II is coupled to the tuned input circuit 49 of the combined detector and oscillator tube I.

The output circuit of tube II may be traced from the anode 2| through the primary winding 53 of a radio frequency transformer 55, and through a conductor 51 to a point of positive potential on the voltage divider 59 of the power supply (H.

The tuned input or selecting circuit 49 for the first detector is similar to the tuned radio frequency circuit 23 above described, and comprises the secondary winding 63 of the radio frequency transformer 55 shunted by a variable condenser 65, which is one unit of the above-mentioned gang condenser. The tuning condenser 65 is shunted by the usual trimmer condenser 51.

The tuned input circuit 49 is coupled to the input electrodes of the detector by means of a conductor 69 which connects the upper terminal of the secondary winding 53 to the control grid I I, and by means of the coupling condenser 39 which connects the lower end of the secondary winding 63 to the cathode I3. The connection through the coupling capacity 39 may be traced from the lower end of the secondary winding 63 through ground, through the condenser 39 and through the conductors I5 and TI to the cathode I3.

A switch I9 is provided for short circuiting the lower portion of the secondary winding 63 for the purpose of making the input circuit 49 tunable over the high frequency range. Another switch BI is provided for shunting another trimmer condenser 83 across the tuning condenser 65 at the same time that the short circuiting switch I9 is closed.

Also, when the switch 8i is closed, a small coupling capacity 85 is connected between the upper end of the primary winding 53 and the upper end of the secondary winding 63 for providing the desired transfer of energy at the high frequencies.

The proper negative bias is supplied to the grids I5 and II of the amplifier and detector tubes, respectively, by means of the lower section 81 of the voltage divider 59, the cathodes I3 and 73 being connected through conductors I5 and TI and a conductor 89 to a positive point near the lower end of the voltage divider and the grids I 5 and II being connected through ground to the lower end of the voltage divider.

The detector electrodes, which are enclosed in the same container with the oscillator electrodes, comprise the cathode I3 and control grid lI, above referred to, a screen grid 9! and an anode 93. Both the screen grid 9| and the screen grid ll of the radio frequency amplifier tube II are supplied with positive potential from a point on the voltage divider 59. They have a radio frequency connection to ground through a bypass condenser 95.

The anode 93 is connected to: the upper end of the primary 9? of a tuned intermediate frequency transformer 99, the lower end of which is connected to a positive point on the voltage divider 59 through a conductor IUI. The primary winding 91 and the primary winding 53 both have a radio frequency connection to ground through the bypass condenser I 90.

The oscillator electrodes consist of a control grid I93, an anode I05, and the cathode 13 which is common to the detector and oscillator. By utilizing a common cathode, the detector and oscillator are coupled through the common electron stream.

The frequency determining circuit of the oscillator comprises an inductance coil Iii? which is shunted by a variable condenser I99 and a fixed condenser II! connected in series, the fixed condenser III having a larger capacity than the maximum capacity of the variable condenser I99. The variable condenser I59 is one unit of the above-mentioned gang condenser, and is variable simultaneously with the condensers 33 and 65 by means of a common tuning control, as indicated by the dotted line H3.

The fixed condenser I II is employed in series with the variable condenser I09 for the purpose of making the oscillator track with the tuned.

radio frequency circuits, as described in Carlson Patent No. 1,740,331, and forms no part of our invention. By "tracking the oscillator with the tuned radio frequency circuits is meant so adjusting the oscillator that its oscillations always.

have a constant frequency difference from that to which the radio frequency circuits are tuned.

The variable condenser I99 is shunted by a trimmer condenser M5 for lining-up the oscillator with the tuned radio frequency circuits 23 and 49 in the broadcast band. A switch II! is provided for shunting another trimmer condenser H9 across the variable condenser 599 when the receiver is set to receive signals in the higher frequency band.

The upper end of the inductance coil I9! is coupled to the oscillator control grid I93 through a coupling capacity I2I, while the point between the fixed condenser iii and the variable condenser !99 is connected to the cathode I3 through ground, the bypass condenser 39, and the conductors I5 and TI.

An oscillator grid leak resistor I23 is connected between the grid 593 and the cathode I3.

The plate circuit of the oscillator is coupled to the tuned grid circuit for producing sustained oscillations by means of an inductance coil I212. The plate circuit of the oscillator may be traced from the plate I95 through the inductance coil I25, and through a voltage reducing resistor I21 through conductor I9! to the voltage divider 59. A radio frequency connection from the lower end of coil I25 to ground is provided by a bypass condenser I28.

The oscillator tuned circuit and tuned radio frequency circuits 23 and 49 are so adjusted with respect to each other that in the broadcast band, the incoming signal beats with the fundamental frequency of the oscillator to produce a signal at an intermediate frequency, which in a preferredernbodiment is 175 kilocycles. This intermediate frequency output is transferred to the second detector I29 by means of the tuned intermediate frequency transformer 99.

When receiving within the police hand, all of the above-mentioned switches are closed, whereby the radio frequency circuits are tunable over the police band range and properly lined-up with the oscilllator. When receiving within this frequency range, the second harmonic of the oscillater is utilized.

The relation between the tuned radio frequency circuits 23 and 49 and the oscillator, with the switches closed, is such that the incoming signals beat with the second harmonic'of the oscillator to produce the same intermediate frequency as produced in broadcast reception.

In the particular embodiment being described, the second harmonic frequency of the oscillator is always 1'75 kilocycles higher than the frequency to which the radio-frequency circuits 23 and 49 are tuned when the switches are closed. With the switches open, the fundamental frequency of the oscillator is always 1'75 kilocycles higher than the frequency to which said circuits 23 and 49 are tuned.

In accordance with another embodiment of our invention, the selecting circuit is so adjusted with respect to the oscillator that in the broadcast band the oscillator frequency is 1'75 kilocycles above the frequency of the selected signal, while in the police band the harmonic frequency of the oscillator is 175 kilocycles below the selected signal. This extends the range for police band reception while retaining, at the same time, the advantages of having the oscillator frequency higher than the signal frequency in the broadcast band.

That the above-described adjustment permits the reception of signals at a higher frequency than permitted by the first-descriMd adjustment is obvious since in the one case the signal received is 175 kilocycles above the harmonic frequency, while in the other case the signal is 175 kilocycles below it. As to the adjustment in the broadcast band, it is well known that, when employing a high intermediate frequency, it is difficult to make the oscillator cover the desired frequency range if it is adjusted to oscillate at a frequency lower than that of the incoming signal.

The circuit shown in Fig. 2 is the same as that shown in Fig. l, with the present preferred form of radio frequency coil structure and switch and trimmer condenser construction included therein. In the two figures, like reference numerals indicate like parts.

Referring to Fig. 2, the radio frequency trans-- former 25 comprises a universal Wound coil 27 which forms the primary of the transformer. The secondary 29 of the transformer consists of four universal wound coils connected in series and mounted below the primary coil 21. A tap connection 26 extends from a connection between two of the coils to permit short circuiting the two lower universal wound coils when receiving in the police band range.

The radio frequency transformer 55 is identical in construction with the transformer 25 above described.

The switch structure for switching from one frequency range to another comprises a base plate I3I having two end plates I33 and I35. Side members I 31 and I39 of insulating material are fastened to the end plates I33 and I35 for supporting the switches and police band trimmer condensers.

In order to prevent undesired capacity coupling, the switch structure is divided intosections by means of shielding plates I4: and I43 which are supported from the base member I35 and electrically connected thereto. are also electrically connected to a grounded metal plate I45 on the outside of the side member Iti.

The first section includes the short circuiting switch 4I and the trimmer condenser switch 4-3 of the first tuned radio-frequency circuit. The contact points Ma and 43a of the switches 41 and 43, respectively, comprise strip elements riveted to the side member I39. The switch arm 345 of the short circuiting switch MB of the short circuiting switch 4| comprises a strip of springy metal riveted to the side member I31 and electrically connected to the grounded metal plate 545. The switch arm 436 of the trimmer condenser switch 43 comprises a strip of springy metal riveted to the side member I31.

The trimmer condenser 45 is mounted on the side member I3! and comprises a condenser plate of flexible spring metal Ml positioned over the grounded plate I45 (which forms the other condenser plate) anol insulated therefrom by means of a piece of mica I49. The upper end of the trimmer condenser plate M1 is riveted to the side member I3? and electrically connected to the switch arm 436. The spacing between the trimmer condenser plate I41 and the grounded plate I45 is made adjustable by means of a screw bolt 5! which is threaded into the side member I3? whereby the head of the screw bolt can be made to engage the condenser plate M1.

The coupling condenser 41 is supported from the side members I31 and I39 and has one terminal electrically connected to the switch arm 43B and the other terminal electrically connected to a piece of strip metal I53 riveted to the side member I39.

It will be noted that the switch contact point 43a is a small piece of metal so that although it is connected to the grid I5 at all times, it has no detrimental effect since the capacity to ground is very small.

The construction of the short circuiting switch I9, the trimmer condenser switch 81, and the coupling condenser in the second switch section is the same as the corresponding elements in the first section.

The third section includes only a trimmer condenser II9 which is connected in the oscillator c rcuit, and its switch III. The construction of the trimmer condenser H9 and the switch II! is the same as that of the trimmer condensers and switches in the other sections.

All of the switch arms are moved upwardly to close the switches simultaneously when a shaft I55 is rotated. A knob i5! is provided for rotating the shaft. Shaft I55 is journaled in the end plates I33 and I35 and has a fiat strip 159 of insulating material fastened thereon and so positioned with respect to the switch arms that when the switches are open, the switch arms are resting against the flat side of the strip. When the shaft I55 is given a quarter turn, the edge of the strip I59 is brought into contact with the switch arms to force them upwardly and close all the switches.

It will be evident that, since the rotors of condensers 33, 65 and W9 are units of a gang condenser and mounted upon a common shaft for simultaneous rotation, the radio-frequency and oscillator circuits must be lined-up for both of the frequency ranges. That is, in both frequency ranges the radio-frequency circuits 23 and 39 must always be tuned to the same frequency; in the broadcast band, the fundamental frequency of the oscillator must always be 175 kilocycles above the frequency to which circuits 23 and E9 are tuned, and in the police band the second harmonic of the oscillator must always be 1'75 kilocycles above the frequency to which circuits 23 and 49 are tuned.

The method by which the circuits are linedup is as follows: Before the receiver is assembled the condensers 33, 65 and 509 are adjusted in the usual manner to make them of equal capacity at all settings of the rotors. The transformer secondaries 29 and 55 are compared with a standard coil before assembly and so adjusted that they will have the same inductance values.

In accordance with one feature of our invention, the secondary coils 29 and 63 are adjusted as follows: Taking secondary 29 as an example, the two lower universal wound coils are short circuited and the two upper universal wound coils of. secondary 29 are compared with the standard inductance coil for the police band and the combined inductance of these two coils brought to the correct value by adjusting the spacing between them.

Next the short-circuit is removed from the two lower coils and the four coils of secondary 29 are compared with the standard inductance coil for the broadcast band. The combined inductance of the four coils is brought to the corr-ect value by adjusting the spacing between the two lower coils by moving the lowest coil, the spacing of the previously adjusted two upper coils remaining unchanged.

It will be seen that by following the abovedescribed procedure, the second adjustment of the secondary coil inductance does not materially affect the first or police band adjustment because the coils involved in the second adjustment are short-circuited during operation over the police band. While the procedure has been described as applied to coils having concentrated windings, it will be understood that it may be applied equally well to solenoid coils where sec tions of a coil winding are spaced apart to permit adjustment of the inductance.

The lineup is completed after the receiver is assembled by opening all the switches and setting the tuning condensers 33, G5, and Ill9 near the minimum capacity position, adjusting the trimmer condensers 35 and 67 until the radio frequency circuits 23 and 49 are tuned to the same frequency, and adjusting trimmer condenser II5 until the oscillator frequency is I kilocycles above the frequency to which circuits 23 and 49 are tuned. This completes the lineup for the broadcast band.

Next the line-up for the police band is completed by closing all the switches (by giving knob I57 a quarter turn) and adjusting the trimmer condensers 45 and 83 until circuits 23 and 49 are tuned to the same frequency. The trimmer condenser II9 is then adjusted until the second harmonic of the oscillator is kilocycles above the frequency to which circuits 23 and 49 are tuned.

From the foregoing, it will be apparent that the receiver may be lined-up accurately for both frequency bands and that the lining-up operation for one frequency band does not affect the line-up for the other frequency band.

Referring to Fig. 3, there is shown a modified tuned radio frequency circuit which may be utilized in place of the circuit shown in Figs. 1 and 2, for obtaining a more exact line-up between the oscillator and radio frequency circuits at the higher frequencies. The circuit is the same as that shown in Fig. 1, (like reference numerals indicating like parts), except that a fixed condenser IGI is connected in series with the tuning condenser 33 and shunted by a switch I63, which is closed when receiving within the broadcast band and open when receiving within the police or high frequency band.

The condenser I6I preferably is given a capacity which is larger than the maximum capacity of the tuning condenser (approximately twice as large, for example) and is utilized to provide more exact line-up of the radio frequency circuits with the second harmonic ofv the oscillator at the lower frequency end of the police band.

Another form of tuned radio frequency circuit which may be utilized in place of the one shown in Figs. 1 and 2 is the circuit shown in Fig. 4. In these figures the same reference numerals indicate like parts. In Fig. l, the circuit includes a separate set of secondary windings for each frequency range. The secondary coils I65 and IE1, which comprise the secondary winding I69 for the police band, are mounted above the primary coil HI and shunted by a trimmer condenser I I3 and a short circuiting switch I15.

The secondary coils I'I'I, its and IBI, which comprise the secondary winding I82 for the broadcast range, are located below the primary winding Ill and are shunted by a short circuit ing switch I83.

The lower ends of secondary windings I69 and I82 are connected to ground as indicated by the conventional symbol I85. The upper ends of the secondary windings I 99 and I 82 are connected to the switch points I81 and I89, respectively, so that a tuning condenser 33, shunted by the usual trimmer condenser 35, may be connected across either one of the secondary windings by means of the switch arm I93. vent undesirable absorption of energy, the switches are so arranged that when one secondary winding is in use, the other secondary Winding is short circuited.

In order to provide the desired transfer of energy when receiving in the high frequency range, a coupling condenser AI is connected between the antenna 3! and the upper end of the secondary winding I59, by means of a switch I95.

The above-described circuit, and, in particular, the circuit shown in Figs. 1 and 2, may be. modifled to permit both more exact tracking of the oscillator and the radio frequency circuits, and the utilization of automatic volume control as shown in Fig. 5. In these figures, like reference numerals indicate like parts.

Referring to Fig. 5 it will be seen that the tuned radio frequency amplifier circuit of the receiver differs from that shown in Fig. l in that a blocking condenser I99 is inserted in the connection between the lower end of the coil 29 and the connection to ground to permit application of a volume control bias to the grid of the tube.

The volume control bias is applied to the grid through a resistor I94 which is connected to any In order to presuitable source of automatic volume control bias as indicated by the legend. A suitable. constant bias for the grid is supplied in a conventional manner by means of the resistor I98 in the cathode circuit.

Instead of shorting the lower portion of coil 29 directly through the switch 41, it is shorted with respect to radio frequency energy through the condenser E96 and a series tracking condenser I91. When the switch 4'! is closed, the condenser I96 is in series with the tuning condenser 33 and functions the same as condenser [6| in Fig. 3 and condenser III in Fig. 1.

By connecting the series tracking condenser in series with the short-circuiting switch as shown in Fig. 5, the addition of an extra switch is avoided. This will be seen from a comparison of Figs. 3 and 5.

By employing our invention, a small receiver may be made tunable over a wide range in a high frequency band as well as tunable over the usual broadcast band, merely by the addition of a few small condensers and switches. Because of the small size and the small number of the additional parts required, such a multi-range receiver is compact and only slightly more expensive to manufacture than a receiver tunable over the broadcast band only,

Also, our invention makes it possible to lineup the tuned radio frequency circuits and the oscillator over the different frequency bands just as easily as the several circuits are lined-up for one frequency band. This feature is of great importance in obtaining economical assembly of the receivers.

Various modifications, other than those described, may be made in our invention without departing from the spirit and scope thereof, and we desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art, and set forth in the appended claims.

We claim as our invention:

1. The method of adjusting the tunable circuits of a radio receiver for simultaneous tuning adjustment by a tuning control means common to said circuits, one of said circuits including an inductance coil wound in at least four sections, said method including the steps of short-circuiting two of said sections and adjusting the inductive relation between the remaining two sections until they have a combined predetermined inductance value, and removing said short-cincuit and adjusting the inductive relation between said two remaining coil sections until all the sections of said coil have a second combined predetermined value.

2. The method of adjusting the. tunable circuits of a radio receiver for simultaneous tuning control, one of said circuits including an inductance coil wound in at least four spaced sections, said method including the steps of short-circuiting two of said sections and adjusting the spacing between the remaining two coil sections until they have a combined predetermined inductance value, and removing said short-circuit and adjusting the spacing between said remaining two coil sections until all of the sections of said coil have a second combined predetermined inductance value.

3. In a superheterodyne receiver having a tunable radio-frequency circuit and an oscillator having a tunable circuit, said radio-frequency circuit including an inductance coil, means for shortcircuiting a section thereof, and a trimmer condenser, the method of lining-up said tunable circuits for obtaining a desired intermediate frequency throughout two frequency ranges by the operation of a single tuning control common to said tunable circuits, which method comprises the steps of lining-up said tunable circuits for one of said frequency ranges with all of said inductance coil included in said radio-frequency circuit, and then short-circuiting said coil section, connecting said trimmer condenser across said inductance coil, and lining-up said tunable circuit for the other of said frequency ranges by adjusting said trimmer condenser.

4. In a radio receiver, a plurality of tunable selecting circuits connected in cascade, each selecting circuit comprising an inductance coil shunted by a variable tuning condenser, a trimmer condenser connected in parallel with each tuning condenser, additional trimmer condensers, one for each of said tuning condensers, a coupling condenser associated with each selecting circuit, and a simultaneous control means for short-circuiting a portion of each of said inductance coils, for connecting said additional trimmer condensers across said tuning condensers and for connecting said coupling condensers to said selecting circuits.

5. A radio receiver according to claim 4 characterized in that said simultaneous control means comprises a unitary switch structure consisting of a plurality of electrostatically shielded switch sections, each section including the switches and the additional trimmer condenser for one of said selecting circuits, said additional trimmer condenser being an integral part of said switch structure.

KENNETH A. CHITTICK. WILLIAM H. CONRON. 

